The invention deals with a method and apparatus for detecting defective leads of a component which has been mounted on a circuit board prior to trimming the leads and/or bending (clinching) the leads to the underside of the circuit board, and particularly to detecting the leads of a multi-lead electronic component such as a dual in-line package (DIP).
DIP components comprise parallel rows of leads projecting from each side of the component, with anywhere from two to twenty one leads in each row. In high volume, mechanized population of circuit boards with electronic components, there exists the need for trimming excess portions of the leads which extend through the circuit board and bending or forming (clinching) the remaining portions of the leads to the underside of the circuit board prior to soldering, such as by-flow soldering. U.S. Pat. No. 4,151,637 is exemplary of a device for cutting and clinching inwardly or outwardly and for varying the machine according to the center distances of opposed leads; and the subject matter of this patent is incorporated herein by reference.
Defects such as missing or bent leads result in misinsertions. Upon insertion of the lead through a hole of the circuit board, it is also possible that an insufficient amount of the lead is presented for a subsequent soldering operation. Accordingly, the instant invention provides means for detecting such misinserted and defective leads prior to clinching and/or cutting thereof, such that a programmed controller for the overall operation may receive information regarding the defect and halt or change processing of the circuit board according to a particular program used.
Of the above-referenced prior art, only U.S. Pat. Nos. 4,499,649 and 4,549,087 disclose a method and means for cutting and clinching leads immediately after detecting the presence of all leads. However, lead presence is detected by reflection of light off of the lead directly, requiring that the light emitter and receiver be provided in a package which is disposed very close to the circuit board and thus is more likely damaged and/or dirtied by the dust and debris generally associated with lead cutting.
Japanese Patent Application No. 56-136698 discloses a device which also relies upon the direct presence or absence of a lead of a component, such that an acceptable lead must interrupt a light beam. The particular configuration of this device, along with the necessity for sensing the leads directly, does not provide easy adaptability of such a detection method or apparatus to a cut and/or clinch mechanism.
U.S. Pat. No. 4,286,379 provides a means for detecting whether or not all of the leads of the component have been inserted properly into a circuit board with the detection of properly inserted leads being performed during the forming or clinching of leads of the component to the underside of the circuit board. Plural pivotal forming or clinching levers, one for each lead, are provided with apertures through which light-emitting elements can communicate with light-receiving elements when all of the levers have been properly displaced by engagement with acceptable component leads. When a lead does not extend below the circuit board, displacement of the lever corresponding to that lead does not occur, and that lever will block light transmission and provide an indication of a defect. The complexity of the forming and detecting head of this device prevents, or at least limits, any provision for lead trimming. Furthermore, the spring means which biases each lever into the proper position prior to lead engagement presents an engineering design problem in that the leaf material of the springs must be very lightweight when used on soft leads in order to assure a positive displacement or deflection of the levers by the soft leads. Thus, without constant cleaning of the tooling assembly, any contamination built up therein could affect the springs and/or photosensors.
U.S. Pat. No. 4,621,419 discloses a lead detector in FIG. 4 in which there is a plunger provided for each lead that is inserted through a circuit board hole. An acceptable lead depresses a corresponding spring biased so that the lower portion of the plunger will block a slider from moving in a direction perpendicular to the direction of movement of the plunger and thus prevent interruption of a light beam by the slider. An unacceptable lead fails to depress the plunger sufficiently to block movement of the slide, resulting in an unobstructed light beam providing an indication of a defective lead. This device also is not disclosed as part of, nor is it readily adaptable to, a out and clinch device.
Japanese Patent Application No. 55-97542 discloses a lead detector and bender (clincher) for the leads of parts such as integrated circuits mounted on a circuit board. A vertically recriprocatable support member 2 has plungers 6, each of which is normally biased to an extended position of FIG. 1 by compression springs 5. Upon insertion of the leads of the component through the holes of the circuit board, support member 2 is raised to contact plunger 6 with the ends of the inserted leads and thus to depress the plunger 6 against the biasing of springs 5. As seen in FIG. 2 of this reference, an acceptable lead will allow a beam of light to pass between members 8 and 9 through a hole 7 of the plunger 6 to indicate acceptance of the lead. Of course, a defective lead would not depress the plunger sufficiently for the light beam to be made. Thereafter, member 2 is retracted so that the leads may be clinched upon extension of members 11.
The method and apparatus of this prior art reference has a significant defect in that an individual spring is used for each plunger. There is a strong possibility of interference between springs when dealing with DIPs which have upwards of 40 leads and center-to-center spacings of 0.100 inches so that the plungers must be arranged in sliding engagement side-by-side. Further, the device of this reference is only able to clinch inwardly, whereas the instant invention can clinch both inwardly and outwardly as well as provide the trimming function that the prior art reference can not provide. Also, by having the transmitter and receiver of each plunger spaced on opposite sides of the plunger, additional space is required for the block 2.
Thus, these prior art sensors can be categorized generally as utilizing: (i) a direct method of interrupting or reflecting at least one light beam by at least one lead, or (ii) an indirect method of sensing the leads by sensing the status of pins or levers which are interposed between the leads and light beams.
With the direct sensing method, the actual sensing is done in a contaminated area so that the sensors are subject to failure due to contamination. Typically, leads protruding beyond the bottom surface of the circuit board by less than 0.050 inches are insufficiently long to interrupt the light beams, whether or not they are sufficiently long for clinching and soldering.
In the indirect sensing devices, the interposers for contacting the leads are generally spring-biased and the spring forces are held to a minimum in order to keep from bending the leads. Thus the slightest contamination can cause failure of the springs. Still further, it is necessary to replace the springs in order to selectively vary the forces applied to the leads.
Accordingly, it is an object of the instant invention to obviate the contamination problems inherent in prior art direct and indirect sensors.
It is also an object of the invention to provide selective variation of the forces applied to the leads in order to perform such detection without requiring interchange of parts or disassembly of the device.
It is a further object of the invention to provide for adjustment of the device to various lead lengths and/or anvil heights.
Still further, it is an object of the invention to redirect and guide light via an interposer so as to allow the light transmitter and receiver to be positioned on the same side of a mirrored half of the device. Such an arrangement supports different variable spacing of the halves commensurate with the center distances between leads on opposite sides or ends of a component, while also facilitating inward and outward cut and clinch capabilities of the device.
These and other objects of the invention may be understood from the remaining disclosure.